The present invention relates to an interlock mechanism and has particular relevance to such an interlock mechanism as used on a composite power tool formed from a body able to accept and one of a plurality of interchangeable heads. Each one of the heads may couple with the body to provide a power tool capable of achieving a dedicated task determined by the head.
In EP-A-899,063 there is shown a power tool system formed from a common body and a plurality of tool heads, each of which is selectively mountable on the body. Each head is designed to achieve a different function, such as drilling, sanding or sawing.
The manner in which the heads attach to the body is important. The coupling between the head and the body must be firm enough to permit efficient transmission of torque from the body to the head. However, the coupling also needs to be capable of being released easily by a user of the tool which wishes to change the head for another head in order to achieve a different tool operation.
While the interlock mechanism described in the above patent application functions satisfactorily, release of the mechanism has the potential of being problematical as the user has no way of knowing when the coupling has been broken, thereby not knowing when the tool head is free to be removed from the tool body.
It is an object of the present invention to provide an interlock mechanism which at least alleviates the above shortcomings by provision of an interlock mechanism which provides the user with a positive indication of when the mechanism is released.
Accordingly, the present invention provides an interlock mechanism for releasably coupling first and second portions of a power tool including: a spring normally biassed to a first, closed position; and an actuator co-operable with the spring to urge the spring, under influence of the actuator, into a second, open position. The actuator includes a spring-engaging surface formed from a plurality of individual surfaces which are not coplanar. Provision of the spring-engaging surface with a plurality of individual non-coplanar surfaces enables the interlock mechanism to give a positive indication of being open, rather than the hitherto-known mechanism which employs a linear-style release mechanism which gives the user the indication of the state of operation of the interlock.
In a preferred embodiment the spring-engaging surface defines a dual-gradient structure. Providing a structure with a dual-gradient allows for non-linear movement of the spring between the first, open position and the second, closed position. This means that when the user operates the actuator different rates of movement of the spring between the open and closed positions are possible with the same rate of movement of the actuator dependent upon which gradient of the dual-gradient surface the spring is engaged with.
Additionally or alternatively the spring is formed as a U-shaped member, the open arms of which are co-operable with the actuator. This structure enables an attachment to be coupled by the interlock mechanism by passing between the open arms and being clasped thereby.
Preferably the open arms of the spring contact the spring-engaging surface of the actuator such that movement of the actuator causes concomitant movement of the arms of the spring. This allows the user of the mechanism to activate it simply by operating on the actuator. Preferably the arms of the U-shaped member are not straight.
Advantageously the actuator defines a seat within which at least a portion of the spring sits, the seat including a plurality of parallel members arranged to engage with the at least portion of the spring, thereby to retain the spring in the seat in the first, closed position. This allows the spring to be held in its first, open position by the actuator and hence ready for coupling with an attachment presented to the interlock mechanism without the need for movement of the spring.
Preferably the plurality of parallel members comprise two projections, each of which projections engages with a corresponding one of the open arms of the U-shaped member. Preferably the actuator has a plurality of spring-engaging surfaces. Also each of the arms of the U-shaped member engages with a respective one of the plurality of spring-engaging surfaces.
A preferred embodiment to the present invention will now be described, by way of example only, with reference to the accompanying illustrative drawings in which: